The non-aggression principle (or NAP; also called the non-aggression axiom, the anti-coercion, zero aggression principle or non-initiation of force) is an ethical stance that asserts that aggression is inherently wrong. In this context, "aggression" is defined as initiating or threatening any forcible interference with an individual or individual's property.[1]

In contrast to pacifism, the non-aggression principle does not forbid forceful defense. The non-aggression principle is considered by some to be a defining principle of natural-rights libertarianism

The non-aggression principle has existed in various forms. Although the principle has been traced back as far as antiquity, it was first formally described by this name by the Objectivist philosopher Ayn Rand, and then further popularized by libertarian thinkers.[6][7]

A number of authors have created their own formulation of the non-aggression principle, as shown in the table below.

Jefferson describes the NAP in a letter to Francis Gilmer: "Rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add 'within the limits of the law', because law is often but the tyrant's will, and always so when it violates the rights of the individual." and "No man has a natural right to commit aggression on the equal rights of another, and this is all from which the laws ought to restrain him."[9][10]

In his book On Liberty Mill states the NAP as follows: "the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others".[12]

In the second chapter of his book, Our Enemy, the State, Nock refers to an ancient formulation of the NAP by the legendary king Pausole, who stated it as two laws. The first law was "hurt no man" and the second was "then do as you please".[13]

In an essay called "Man's Rights" in the book The Virtue of Selfishness she formulated "The precondition of a civilized society is the barring of physical force from social relationships. ... In a civilized society, force may be used only in retaliation and only against those who initiate its use."[14][15][16]

"No one may threaten or commit violence ('aggress') against another man's person or property. Violence may be employed only against the man who commits such violence; that is, only defensively against the aggressive violence of another. In short, no violence may be employed against a nonaggressor. Here is the fundamental rule from which can be deduced the entire corpus of libertarian theory." Cited from "War, Peace, and the State" (1963) which appeared in Egalitarianism as a Revolt Against Nature and Other Essays[17]

Christian worldview: There is an emerging Biblical argument that the natural rights of Locke, Rothbard and others are most truly derived from the Biblical principles of self-stewardship and the image of God in man.[citation needed] (In contrast, some ethicists[21] and anthropologists of religion[22] posit that Biblical principles are merely instances of moral systems that have evolved in different places with some common features.) The rights to life, liberty and property derive from the fact that God has granted each person to be the steward of himself and none other, granting him the human authority to manage his own life and property, which morally requires him to do so according to God's Law, but civilly requires him to respect the dignity and property rights of his neighbor. The Biblical purpose of civil government is to serve on behalf of individuals who have had their life, liberty, or property violated by another.

Objectivism: Ayn Rand rejected natural or inborn rights theories as well as supernatural claims and instead proposed a philosophy based on observable reality along with a corresponding ethics based on the factual requirements of human life in a social context.[23] She stressed that the political principle of non-aggression is not a primary and that it only has validity as a consequence of a more fundamental philosophy. For this reason, many of her conclusions differ from others who hold the NAP as an axiom or arrived at it differently. She proposed that man survives by identifying and using concepts in his rational mind since "no sensations, percepts, urges or instincts can do it; only a mind can." She wrote, "since reason is man's basic means of survival, that which is proper to the life of a rational being is the good; that which negates, opposes or destroys it [i.e. initiatory force or fraud] is the evil."[24]

Many supporters and opponents of abortion rights justify their position on NAP grounds. One important question to determine whether or not abortion is consistent with NAP is at what stage of development a fertilized human egg cell can be considered a human being with the status and rights attributed to personhood. Some supporters of NAP argue this occurs at the moment of conception. Others argue that since they believe the fetus lacks sentience until a certain stage of development, it does not qualify as a human being, and as such may be considered property of the mother. Opponents of abortion, on the other hand, state sentience is not a qualifying factor. They refer to the animal rights discussion and point out the Argument from marginal cases that concludes NAP also applies to non-sentient (i.e. mentally handicapped) humans.[26]

Another important question is whether an unwelcome fetus should be considered to be an unauthorized trespasser in its mother's body.[27] The non-aggression principle does not protect trespassers from the owners of the property on which they are trespassing.[28] It can also be argued that unwelcome fetuses are themselves committing aggression against their mothers, by taking materials (oxygen, water, nutrients) from her bloodstream, by injecting toxic metabolic end-products (carbon dioxide and creatinine) into her bloodstream, and by preparing to subject her to major medical/surgical trauma in the form of full-term labor and delivery.

Objectivist philosopher Leonard Peikoff has argued that a fetus has no right to life inside the womb because it is not an "independently existing, biologically formed organism, let alone a person."[29] Pro-choice libertarian Murray Rothbard held the same stance, maintaining that abortion is justified at any time during pregnancy if the fetus is no longer welcome inside its mother.[30] Likewise, other pro-choice supporters base their argument on criminal trespass.[31] In that case, they claim, NAP is not violated when the fetus is forcibly removed, with deadly force if need be, from the mother’s body, just as NAP is not violated when an owner removes from the owner’s property an unwanted visitor who is not willing to leave voluntarily. Libertarian theorist Walter Block follows this line of argument but makes a distinction between evicting the fetus prematurely so that it dies and actively killing it (see Libertarian perspectives on abortion).

Pro-life libertarians, however, argue that because the parents were actively involved in creating a new human life and that life has not consented to his or her own existence, that life is in the womb by necessity and no parasitism or trespassing is involved (see also legal necessity). They state that as the parents are responsible for that life's position, NAP would be violated when that life is killed with abortive techniques.

NAP is defined as applicable to any unauthorized actions towards a person’s physical property. Supporters of NAP disagree on whether it should apply to intellectual property (IP) rights as well as physical property rights.[32] Some argue that because intellectual concepts are non-rivalrous, intellectual property rights are unnecessary.[33] while others argue that intellectual property rights are as valid and important as physical ones.[34]

Some libertarians justify the existence of a minimalstate on the grounds that anarchism implies that the non-aggression principle is optional because the enforcement of laws is open to competition.[57] They claim competing law enforcement would always result in war and the rule of the most powerful.

Anarcho-capitalists usually respond to this argument that this presumed outcome of coercive competition (e.g. PMCs or PDAs that enforce local law) is not likely because of the very high cost, in lives and economically, of war. They claim that war drains those involved and leaves non-combatant parties as the most powerful, economically and militarily, ready to take over.[58][59][60] Therefore, anarcho-capitalists claim that in practice, and in more advanced societies with large institutions that have a responsibility to protect their vested interests, disputes are most likely to be settled peacefully.[61][62] Anarcho-capitalists also point out that a state monopoly of law enforcement does not necessarily make NAP present throughout society as corruption and corporatism, as well as lobby groupclientelism in democracies, favor only certain people or organizations. Anarcho-capitalists aligned with the Rothbardian philosophy generally contend that the state violates the non-aggression principle by its very nature because, it is argued, governments necessarily use force against those who have not stolen private property, vandalized private property, assaulted anyone, or committed fraud.[61][63][64]

Anarcho-capitalists argue that the protection of individuals against aggression is self-sustaining like any other valuable service, and that it can be supplied without coercion by the free market much more effectively and efficiently than by a government monopoly.[65] Their approach, based on proportionality in justice and damagecompensation, argues that full restitution is compatible with both retributivism and a utilitarian degree of deterrence while consistently maintaining NAP in a society.[59][66][67] They extend their argument to all public goods and services traditionally funded through taxation, like security offered by dikes.[68]

NAP faces two kinds of criticism: the first holds that the principle is immoral, and the second argues that it is impossible to apply consistently in practice; respectively, consequentialist or deontological criticisms, and inconsistency criticisms. Libertarian academic philosophers have noted the implausible results consistently applying the principle yields: for example, Professor Matt Zwolinski notes that, because pollution necessarily violates the NAP by encroaching (even if slightly) on other people's property, consistently applying the NAP would prohibit driving, starting a fire, and other activities necessary to the maintenance of industrial society.[70]

Critics argue that the non-aggression principle is not ethical because it opposes the initiation of force even when they would consider the results of such initiation to be morally superior to the alternatives that they have identified. In arguing against the NAP, philosopher Matt Zwolinski has proposed the following scenario: "Suppose that by imposing a very, very small tax on billionaires, I could provide life-saving vaccination for tens of thousands of desperately poor children. Even if we grant that taxation is aggression, and that aggression is generally wrong, is it really so obvious that the relatively minor aggression involved in these examples is wrong, given the tremendous benefit it produces?"[70]

Incompatibility with driving and other civilizational necessities[edit]

Zwolinski also notes that the NAP is incompatible with any practice that produces any pollution, because pollution encroaches on the property rights of others. Therefore, the NAP prohibits both driving and starting fires. Citing Professor David Friedman, Professor Zwolinski notes that the NAP is unable to place a sensible limitation on risk-creating behavior. Writes Zwolinski,

Of course, almost everything we do imposes some risk of harm on innocent persons. We run this risk when we drive on the highway (what if we suffer a heart attack, or become distracted), or when we fly airplanes over populated areas. Most of us think that some of these risks are justifiable, while others are not, and that the difference between them has something to do with the size and likelihood of the risked harm, the importance of the risky activity, and the availability and cost of less risky activities. But considerations like this carry zero weight in the NAP’s absolute prohibition on aggression. That principle seems compatible with only two possible rules: either all risks are permissible (because they are not really aggression until they actually result in a harm), or none are (because they are). And neither of these seems sensible.

Some critics use the example of the trolley problem to invalidate NAP. In case of the runaway trolley, headed for five victims tied to the track, NAP does not allow a trolley passenger to flip the switch that diverts the trolley to a different track if there is a person tied to that track. That person would have been unharmed if nothing was done, therefore by flipping the switch NAP is violated. Another example often cited by critics is human shields.

Some supporters argue that no one initiates force if their only option for self-defense is to use force against a greater number of people as long as they were not responsible for being in the position they are in. Murray Rothbard's and Walter Block's formulations of NAP avoid these objections by either specifying that the NAP applies only to a civilized context (and not 'lifeboat situations') or that it applies only to legal rights (as opposed to general morality). Thus a starving man may, in consonance with general morality, break into a hunting cabin and steal food, but nevertheless he is aggressing, i.e. violating the NAP, and (by most rectification theories) should pay compensation.[71] Critics argue that the legal rights approach might allow people who can afford to pay a sufficiently large amount of compensation to get away with murder. They point out that local law, though based on NAP, may vary from proportional compensation to capital punishment to no compensation at all.[59]

Other critics state that the NAP is unethical because it does not provide for the violent prohibition of, and thereby supposedly legitimizes, several forms of aggression that do not involve intrusion on property rights, such as verbal sexual harassment, defamation, boycotting, noninvasive striking, and noninvasive discrimination. If a victim thus provoked would turn to physical violence, according to the NAP, he would be labeled an aggressor. Supporters of the NAP, however, state that boycotting[72][73] and defamation[74][75] both constitute freedoms of speech and that boycotting,[72][73] noninvasive striking,[73][76] and noninvasive discrimination[77] all constitute freedoms of association, and that both freedoms of association and of speech are nonaggressive. Supporters also point out that prohibiting physical retaliation against an action is not itself condonementof said action,[78] and that generally there are other, nonphysical means by which one can combat social ills (e.g., discrimination) that do not violate the NAP.[73][77] Some supporters also state that while, most of the time, individuals choose voluntarily to engage in situations that may cause some degree of mental battering, this mental battering begins, when it cannot be avoided, to constitute unauthorized physical overload of the senses (i.e., eardrum and retina) and that the NAP, at that point, does apply.

Many supporters consider verbal and written threats of imminent physical violence sufficient justification for a defensive response in a physical manner.[79][80] Such threats would then constitute a legitimate limit to permissible speech. Because freedom of association entails the right of owners to choose who is permitted to enter or remain on their premises, legitimate property owners may also impose limitation on speech. For example, the owner of a theatre, wishing to avoid a stampede, may prohibit those on her property from calling ‘fire!’ without just cause.[81] The owner of a bank, however, may not prohibit anyone from urging the general public to a bank run,[72] except insofar as this occurs on the property of said owner.

H.L. Mencken, a writer who influenced many libertarians, puts an ethical limit on the freedom of speech:

I believe there is a limit beyond which free speech cannot go, but it's a limit that's very seldom mentioned. It's the point where free speech begins to collide with the right to privacy. I do not think there are any other conditions to free speech. I've got a right to say and believe anything I please, but I have not got a right to press it on anybody else. [...] Nobody's got a right to be a nuisance to his neighbors.

Supporters also consider physical threats of imminent physical violence (e.g., pointing a firearm at innocent people, stocking up nuclear weapons that cannot be used discriminately against specific individual aggressors) sufficient justification for a defensive response in a physical manner.[83][84][80] Such threats would then constitute a legitimate limit to permissible action.

Critics argue it is not possible to uphold NAP when protecting the environment as most pollution can never be traced back to the party that caused it. They therefore claim that only general broad government regulations will be able to protect the environment. Supporters cite the problem of the tragedy of the commons and argue that free-market environmentalism will be much more effective in conserving nature.[85][86]
Political theorist Hillel Steiner emphasizes that all things made come from natural resources and that the validity of any rights to those made things depends on the validity of the rights to the natural resources.[87] If land was stolen then anyone buying produce from that land would not be the legitimate owner of the goods. Also, if natural resources cannot be privately owned but are, and always will be, the property of all of mankind then NAP would be violated if such a resource would be used without everybody’s consent (see the Lockean proviso and free-market anarchism).[88] Libertarian philosopher Roderick Long points out that, as natural resources are required not only for the production of goods but for the production of the human body as well, the very concept of self-ownership can only exist if the land itself is privately owned.[89]

Consequentialist libertarianDavid Friedman, who believes that the NAP should be understood as a relative rather than absolute principle, defends his view by using a Sorites argument. Friedman begins by stating what he considers obvious: A neighbor aiming his flashlight at someone's property is not aggression, or if it is, it is only aggression in a trivial technical sense. However, aiming at the same property with a gigawatt laser is certainly aggression by any reasonable definition. Yet both flashlight and laser shines photons onto the property, so there must be some cutoff point of how many photons one is permitted to shine upon a property before it is considered aggression. But the cutoff point cannot be found by deduction alone, because of the Sorites paradox, so the non-aggression principle is necessarily ambiguous. Friedman points out the difficulty of undertaking any activity that poses a certain amount of risk to third parties (e.g. flying) if the permission of thousands of people that might be affected by the activity is required.[90]

"Right" has cogently and trenchantly been defined by Professor Sadowsky:

When we say that one has the right to do certain things we mean this and only this, that it would be immoral for another, alone or in combination, to stop him from doing this by the use of physical force or the threat thereof. We do not mean that any use a man makes of his property within the limits set forth is necessarily a moral use?

Sadowsky's definition highlights the crucial distinction we shall make throughout this work between a man's right and the morality or immorality of his exercise of that right. We will contend that it is a man's right to do whatever he wishes with his person; it is his right not to be molested or interfered with by violence from exercising that right. But what may be the moral or immoral ways of exercising that right is a question of personal ethics rather than of political philosophy—which is concerned solely with matters of right, and of the proper or improper exercise of physical violence in human relations. The importance of this crucial distinction cannot be overemphasized. Or, as Elisha Hurlbut concisely put it: "The exercise of a faculty by an individual] is its only use. The manner of its exercise is one thing; that involves a question of morals. The right to its exercise is another thing."